Test out subprocess

subprocess_capture_stderr.py

import subprocess


# http://stackoverflow.com/questions/18774476/subprocess-call-logger-info-and-error-for-stdout-and-stderr-respectively
# http://stackoverflow.com/questions/21953835/run-subprocess-and-print-output-to-logging

def my_buddy_popen():
    """
    Since only stderr is bound, we only get a value for stderr. if this was a good call (exit 0)
    then out _would_ exist and sent to parent's and _not_ be in `out`.
    """
    proc = subprocess.Popen(['ls', '-al', '/tmp/arst/not/exist'], stderr=subprocess.PIPE)
    out, err = proc.communicate()

    print(out)  # None
    print('hallo')
    print(err)

def tryexc1():
    """
    Since stderr hasn't been bound, this uses parent's stderr
    so you see the stderr in your terminal.
    Will additionally raise CalledProcessError and therefore print 'nihao'
    e.output is nothing, even though stderr is bound to stdout
    """
    try:
        subprocess.check_call(['ls', '-al', '/tmp/arstarstarst/'], stdout=subprocess.DEVNULL, stderr=subprocess.STDOUT)
    except subprocess.CalledProcessError as e:
        print(e.output)  # None
        print('nihao')

def tryexc2():
    """
    Since stderr hasn't been bound, this uses parent's stderr
    so you see the stderr in your terminal.
    Will additionally raise CalledProcessError and therefore print 'hello'
    e.output is None
    """
    try:
        subprocess.check_call(['ls', '-al', '/tmp/arstarstarst/'], stdout=subprocess.DEVNULL)
    except subprocess.CalledProcessError as e:
        print(e.output)  # None
        print('hello')

def tryexc_output():
    """
    Since stderr hasn't been bound, this uses parent's stderr
    so you see the stderr in your terminal.
    Will additionally raise CalledProcessError and therefore print 'bonjour'
    e.output is None
    """
    try:
        subprocess.check_output(['ls', '-al', '/tmp/rstarst'])
    except subprocess.CalledProcessError as e:
        print(e.output)  # None
        print('bonjour')

def tryexc_output2():
    """
    Since stderr has been bound to stdout, it gets
    so you see the stderr in your terminal.
    Will additionally raise CalledProcessError and therefore print 'anyonghaseyo'
    e.output contains the stderr of the subproc
    """
    try:
        subprocess.check_output(['ls', '-al', '/tmp/rstarst'], stderr=subprocess.STDOUT)
    except subprocess.CalledProcessError as e:
        print(e.output)  # None
        print('anyonghaseyo')

def tryexc_output3():
    """
    Since stderr has been bound to stdout, it gets added to e.output if it exists.
    Since this is a valid call 'guten tag' is never printed and neither is e.output
    out is the successful output of the call
    NOTE: not assigning 'out' has the nice effect of `tryexc_output2`, that is, the
    output is ignored but the errors can be used in logging for example.
    """
    try:
        out = subprocess.check_output(['ls', '-al', '/tmp/'], stderr=subprocess.STDOUT)
    except subprocess.CalledProcessError as e:
        print(e.output)  # None
        print('guten tag')
    print(out)

def simple():
    """
    Since stderr hasn't been bound, this uses the parent's stderr
    you see the stderr in your terminal.
    """
    subprocess.check_call(['ls', '-al', '/tmp/arstarstarst/'], stdout=subprocess.DEVNULL)

tryexc_output3()